Conjure Siege Engine

You choose a location within range and create a piece of artillery made from pure energy, designed to breach city walls and counter marching armies. You can create either a ballista or a mangonel; both are Large objects, have immunity to poison and psychic damage, and have an AC of 10 + spell mod + proficiency bonus. The caster adds their spell mod to attack and damage rolls made with the engine (not included in below stats). As an action while concentrating on this spell, you can change the form of the engine.

While this spell simplifies the process of usage, the conjured engine still requires multiple individuals operating it to be used effectively. For the purpose of making an attack, it will take an action to aim and an action to fire (the conjured engine creates ammunition and loads itself automatically once per round). Alternatively all users actively operating the engine can use their collective actions to move the engine and themselves up to half their movement speed. The engine cannot be physically moved and fired in the same round.

Another creature within 10ft of the engine can use its action to sight targets for the operators, granting advantage on visible targets and negating disadvantage from indirect targets (such as behind cover). As such, an optimal team of 3 is needed to use the engine per round in combat. The engine has disadvantage on attack rolls against Medium or smaller creatures (a spotter balances this).

-- The ballista form has a +6 to hit, range of 120/480ft, 4d10 force damage, and 60 HP. When attempting to hit an enemy behind cover, it ignores the benefits of half cover. If behind full cover, an attack can still have the possibility of hitting, so long as the cover being used is no more than 6 inches thick.

-- The mangonel form has a +5 to hit, range of 200/800ft (cannot hit targets less than 60ft away from engine), 6d10 force damage, and 120 HP. The high arc of this weapon enables it to hit enemies from above and ignore all horizontal cover bonuses (note that without a spotter, an attack against an enemy behind total cover will still be at disadvantage). Depending on vertical cover (such as a ceiling), the DM may rule a multiple of outcomes, like halved damage or no effect.

Regardless of which form the engine takes, it deals double damage to objects and structures. If the engine is reduced to 0 HP, the spell ends.

Finally, as a bonus action, the caster of this spell can mentally move the engine up to half their movement speed. The crew actively operating the engine move with it when this bonus action is taken, without expending any movement or actions on the crew's part. If the engine is moved this way, it ignores the restriction of being unable to shoot and move in the same round. If the engine is ever more than 120ft from the caster, the spell ends.